01/24/2014

Snow For Part Of The Area Tonight With Several Inches Possible! Your Updated Snowfall Totals Inside...

We have another "clipper" style storm system that will be moving across our area tonight and the data again suggests accumulating snow in our area. The system also has a LOT of wind with it and whatever snow falls will be blowing all over the place on Saturday. This creates quite a few headaches for our area again on Saturday. Let's dive into the latest...

Tonight / Saturday Snow Potential

Our never ending train of storms continues with another moving through tonight. It feels like we have seen one about every 2 days and tonight another brings a chance at accumulating snow and WINDY conditions on Saturday. The data is suggesting a mid level low that approaches our area late tonight and all the computer model data has this low.

The data continues to suggest a solid surge of warmer air on the south side of the low. This is important because when air surges (cold or warm) it causes lift and precipitation. In this case, it will cause snow even thought we are talking about a warm surge. The bottom line is that it is so cold that even a warm surge won't be enough.

Snow Timeline For Tonight / Saturday Morning...

I have to say the data has been extraordinarily consistent for days on end. The higher resolution computer models continue to show a little more precipitation while the lower resolution data shows less precipitation. Regardless of which you believe, all the data suggest it begins in our northern counties slightly after midnight and approaches the river by 3 am, then spreads to our southern counties by 5 am. As you look at the data, notice the timestamp is on the top right part of each image.

Computer Model Snowfall Output

I will tell you, each computer model as been rock steady over the last 3 days or so. If they all agreed, then that would be good but as you will see the NAM computer model continues to show the highest totals. This creates complexity when making a forecast. Have a look...

I wish there was an easy snowfall forecast, but as everyone knows they never are easy. If I was telling you that anywhere from 0.1" to 0.4" of liquid would fall as rain tonight, then I think everyone would say ok. The problem is that range can equal anywhere from 1" of snow to 4" of snow if we have a normal snow to liquid ratio of 10:1 (10" of snow = 1" of liquid). The problem is that the last 2 snowfalls have had snow to liquid to ratios of nearly 25:1 and since we remain cold in the snow producing part of the atmosphere, it seems likely that we will end up with high snow to liquid ratios. The bottom line, is that this forecast is not easy. Let me start by looking at when the snow will fall and then move into how much.

One of the questions I am sure you are asking is why does the NAM show more snow? After analyzing the data for a while this afternoon, I have discovered the difference. The NAM shows a series of two distinct upper lows that move across our area late tonight and tomorrow. The second comes through near daybreak and the NAM is popping a secondary surge of snow on this disturbance. You can see the two tier low well in the image below.

This is where the entire complexity of this forecast lies. Do you believe this two tier structure to the low? I will say this, the NAM is by far the highest resolution computer model of this bunch. It has resolution that the other models simply don't have, so it can resolve things the GFS and EURO computer models simply cannot. Since this secondary low is nothing more than 300 miles wide, there is no way to look at the satellite (water vapor) imagery to identify if it is real. For now, I will forecast a range that allows me to stay close, but if that secondary low verifies, we could need to add 1" to our snowfall range.

When Will The Snow Fall?

The timing still appears to be after midnight tonight and lasting until about mid morning on Saturday. The best snow accumulation potential would be for about 5 hours from sometime around 3 am tonight to around 7 am Saturday morning. It will taper off from north to south on Saturday morning. Another burst of snow appears likely to me as the cold front moves across our area midday and these will be snow bursts. If you catch one, then it will have gusty winds to 40+ mph with brief heavy snow. Any of these bursts can leave an accumulation behind.

How Much Snow Will Fall?

This will obviously be the question everyone is asking. This is a setup that normally leaves the heaviest snow in our northeast counties. While the NAM suggests otherwise, I still feel going with climatology for our area is the best choice. As you look at snowfall totals, remember it is a RANGE so please do not focus on the top number. Remember you have an equal chance to be on the low side of the range as you do on the top side of the range.

1" - 3" Of Snow - This will encompass the bulk of our area including Leitchfield, KY to Munfordville, KY to Lebanon, KY to Bardstown, KY to Shelbyville, KY to Louisville, KY to Shepherdsville, KY to E-town, KY to Hardinsburg, KY to Brandenburg, KY in Kentucky. For Indiana, this includes Tell City, IN to Jasper, IN to Paoli, IN to Bedford, IN to Salem, N to Clarksville, KY To New Albany, IN to Corydon, IN. **I will wait until the late data and adjust this number**

2" - 4" Of Snow - This will occur only in our far eastern and northeastern counties. I have these locations in the higher range... North Vernon, IN to Madison, IN to Bedford, KY to Carrollton, KY to Eminence, KY.

Travel will be adversely affected Saturday morning and you should prepare for a snowy commute in the areas with snow accumulations. Since we have been so cold for so long, anything that falls will stick and the roads Saturday morning will be a mess. On top of the snow, the winds on Saturday will be strong. I have a west wind from 20 - 30 mph and gusting to 40 mph. Notice AdvanceTrak shows wind gusts over 40 mph late on Saturday!

Whether you see a little or a lot of snow on Saturday, it will be blowing all over the place through the day. Blowing and drifting snow is likely, so please use caution.

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Thanks Marc. That was my thinking as well. I'm also thinking the Tuesday night assessment by the NWS of -4 may not be strong enough. With the anticipated snow-pack, I'm thinking -8 might be more realistic (unless, of course, I'm wrong about the snow-pack).
Brrrrr!

You think maybe we'll see the river might freeze again like in the mid 70's by the time this pattern breaks?